08 May 20 7:01:13 PM
Bone marrow is the spongy tissue inside some of the bones in the body, including the hip and thigh bones. Bone marrow contains immature cells, called stem cells. Many people with blood cancers, such as leukemia and lymphoma, sickle cell anemia, and other life-threatening diseases, rely on bone marrow or cord blood transplants to survive. Healthy bone marrow and blood cells are needed in order to live. When disease affects bone marrow so that it can no longer function effectively, a marrow or cord blood transplant could be the best treatment option; for some patients it is the only potential cure.
Fast facts on bone marrow
Here are some key points about bone marrow. More detail is in the main article.
What is bone marrow?
Bone marrow is soft, gelatinous tissue that fills the medullary cavities, the centers of bones. The two types of bone marrow are red bone marrow, known as myeloid tissue, and yellow bone marrow, or fatty tissue. Both types of bone marrow are enriched with blood vessels and capillaries. Bone marrow makes more than 200 billion new blood cells every day.Most blood cells in the body develop from cells in the bone marrow.
Bone marrow stem cells
The bone marrow contains two types of stem cells, mesenchymal and hematopoietic. Red bone marrow consists of a delicate, highly vascular fibrous tissue containing hematopoietic stem cells. These are blood-forming stem cells. Yellow bone marrow contains mesenchymal stem cells, also known as marrow stromal cells. These produce fat, cartilage, and bone. Stem cells are immature cells that can turn into a number of different types of cell.
Hematopoietic stem cells in the bone marrow give rise to two main types of cells: myeloid and lymphoid lineages. These include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, dendritic cells, and megakaryocytes or platelets, as well as T cells, B cells, and natural killer cells. The different types of hematopoietic stem cells vary in their regenerative capacity and potency. Some are multipotent, oligopotent or unipotent as determined by how many types of cell they can create.
Pluripotent hematopoietic stem cells have the following properties:
The process of development of different blood cells from these pluripotent stem cells is known as hematopoiesis. It is these stem cells that are needed in bone marrow transplant.
Stem cells constantly divide and produce new cells. Some new cells remain as stem cells and others go through a series of maturing stages, as precursor or blast cells, before becoming formed, or mature, blood cells. Stem cells rapidly multiply to make millions of blood cells each day. Blood cells have a limited life span. This is around 100-120 days for red blood cells. They are constantly being replaced. The production of healthy stem cells is vital.12
The blood vessels act as a barrier to prevent immature blood cells from leaving the bone marrow. Only mature blood cells contain the membrane proteins required to attach to and pass through the blood vessel endothelium. Hematopoietic stem cells can cross the bone marrow barrier, however. These may be harvested from peripheral, or circulating, blood.15
The blood-forming stem cells in red bone marrow can multiply and mature into three significant types of blood cells, each with their own job:
Once mature, these blood cells move from the marrow into the bloodstream, where they perform important functions required to keep the body alive and healthy. Mesenchymal stem cells are found in the bone marrow cavity. They differentiate into a number of stromal lineages, such as:
Red bone marrow produces all red blood cells and platelets in human adults and around 60 to 70 percent of lymphocytes. Other lymphocytes begin life in the red bone marrow and become fully formed in the lymphatic tissues, including the thymus, spleen, and lymph nodes. Together with the liver and spleen, red bone marrow also plays a role in getting rid of old red blood cells.
Yellow bone marrow mainly acts as a store for fats. It helps to provide sustenance and maintain the correct environment for the bone to function. However, under particular conditions, such as severe blood loss or fever, the yellow marrow may revert to red marrow.
Yellow marrow tends to be located in the central cavities of long bones, and is generally surrounded by a layer of red marrow with long trabeculae (beam-like structures) within a sponge-like reticular framework.
Before birth, bone marrow first develops in the clavicle toward the end of fetal development. It becomes active about 3 weeks later. Bone marrow takes over from the liver as the major hematopoietic organ at 32 to 36 weeks’ gestation. Bone marrow remains red until around the age of 7 years, as the need for new continuous blood formation is high. As the body ages, the red marrow is gradually replaced by yellow fat tissue. Adults have an average of about 2.6 kg (5.7 lbs) of bone marrow, about half of which is red.
In adults, the highest concentration of red marrow is in the bones of the vertebrae, hips (ilium), breastbone (sternum), ribs, skull and at the metaphyseal and epiphyseal ends of the long bones of the arm (humerus) and leg (femur and tibia). All other cancellous, or spongy, bones and central cavities of the long bones are filled with yellow marrow.
Read more about Bone marrow functions
"Written by Hannah Nichols on December 15, 2017"
4/28/2024
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